Silly headcanon: Sandalwood is her older sister, and they are both Rarity’s cousins

Season 9 finale, final scene: it's a cut to several years in the future, where Rarity married a strong guard pony named Silversteel. And she's in a hospital bed.

And in her forelegs? A brown haired tan pony with bright purple eyes.

ROLL CREDITS.

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Then a reboot of Equestria Girls where the next generation features humans with skin tones and hair colors that don't look like they come from a crayon box where suddenly said filly ends up being adopted by two humans through a freak accident across dimensions.

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lol